Process for the manufacture of ammonium nitrate



ril 2 19 p 6 27 H. HOWARD.

PROCESS FOR THE MANUFACTURH OF AMMONIUM NITRATE Filed May 2e. 1926 Patented Apr. 26, lgg..

tasse? HENRY HOWARD, OF CLEVELAND, OHIO, ASSIGNOR TO THE GRASELLI CHEMICAL COMPANY, OF CLEVELAND, OHIO, A' CORPORATION'OF OHIO.

PROCESS FOR THE MANUFACTURE OF AlllI1l![OIl.\l'llfUIlliflf NITRATE.

Application filed May 26,'

This invention relates to a process for the manufacture of ammonium nitrate by the neutralization of nitric acid with ammonia and consists generally in absorbing ammo- 5 nia from a gas mixture,or1ned, for. 1n-

stance, by passing an inert gas such as air in contact with a water solution of ammonia, in a solution of ammonium nitrate, adding nitric acid to the solution of ammonium nitrate to combine with the absorbed ammonia and reusing the unabsorbcd portion of the gas mixture for conveying more ammonia from the water-solution thereof to the 'ammonium nitrate solution in a continuous cycle. v

'lhe principal object of the invention is to devise a simple 'and continuous process in which loss of the reacting materials is avoided.

-Asis well known when a gas comprising ammonia is contacted with a solution of ammonium nitrate and the absorbed ammonia is neutralized by the addition of nitric acid heat is developed and even when the reac- 25 tion conditions are carefully controlled quantities ,of the reagents, which may amount to as much as 10%, are lost. Va-

l rious means have. been devised for avoiding this loss such as the use of a'relu'x condenser operating u on the exit gases i'roin the. an1 monia absor -)er and scrubbing the. exit gases with nitric acid.

In accordance with the (present invention -loss is ositively prevente by the .employ-. ment oipaclosed s stem operated preferab y under slightl reduced pressure at least in those parts w ere losses may occur by leak- "agei- M Thedetailsof the process will be'described in connection with'the operation of anv appa- A ratus suitable for the execution of 'the proct essillustrated in the accompanying drawing. Referrin lto the drawing, yl is a stripping tower to'w ich a water solution of ammonia of say 20%strengthis supplied through the sifght feed devicev19`from a suitable source i o sup 1y represented by the tank 2. 'The wateromwhich the ammonia is stripped in the tower `1 is' discharged through the sealed pipe' 3 to 'Waste andthe ammoma with 192e. serial no. 111,838.

the strip ing gas, such as air, the gas mixture pre erably containing from 20 to 25% of ammonia, passes by wa of the pipe 4 tothe absorber 5. The absor er 5 is o conventional design vand comprises the closed vessel 6, an agitator or stirrer 7 and aI submerged -hood or `distributor 8 und'crwhich -the ammonia containing gas and the nitric 'acid are introduced. Nitric acid of say 50% concentration is'supplie'l to the absorber T M from a source of supply represented by the l tank 9 through the sight feed device 2() and ammonium nitrate liquor produced is discharged from the absorber 5v through the cock l0 and by way of the conduit 11 to the grainers 12., The gases leaving the absorber 5 pass by way of pipe 13 through thescparator 14 from which the retnrnpipe l5 delivers any liquid separated from the gases back into the absorber 5 andthence through 470 the cooler and condenser 16, separator 17, and blower 18 back into the stri )ping tower -1,v thus completing its cycle .o movement.

A ny liquid separated from the gas bythe condenser 16 and separator 171s delivered as imlicatedintothe stripping tower 1.v

. As slated the absorber preferably is maintained under a slightly reduced pressure to avoid losses. 'lhis'may involve a continual slight leakage of air into the system, which l* must be disposed ol and for this purpose. the

breather 2l is provided. Any excess of air in the systenrpasscs through the'small coke filled tower 22 of the breather' where it is scrubbed with water 'supplied' through the sight feed 23 to retain any ammonia in the gases. The resulting water .solution of amj monia is delivered to'the stripping tower 1 while the ammonia-free air passes to the atmosphere through the pipe24. In case a deficiency of air 1n the systemoccurs such as whenthe absorber 5 is operated for a time with a deficiency of nitric acid followedby a correction of -this condition 'the' breather 'device 21 serves to make up this deeiencyby 95 the admission of airthroughvthe pipe 25- and water trap 26. v

Certain details of the a paratus whichmay be used inpractice suc 4ascontroLepr paratus aifddescription of details of the ap- V paratus which is not essential to an understanding of the invention are omitted.

The operation of the process in the apparatus illustrated is as follows:

The water solution of ammonia. is fed into the stripping tower' 1 from the tank 2 at a suitable rate where it is contacted with a countercurret flow of gas from the blower 18A and the resulting gas mixture preferably containing about 20 to 25% of NH.. flows by way of pipe 4 tothe absorber 5 where it is contacted vwith the solution of ammonium nitrate, to which nitric acid is supplied, for instance as 50% nitric acid solution, from the tank 9. Such a 'solution of nitric acid is convenient-ly obtainedby the known process of burning ammonia in the presence ol platinum gauze and condensing andfabsorbing the resulting nitrogen oxi'd gases and the operation of the ammonia stripping tower may be the same as that of the strippingtower. employed for supplying-the ammonia containing gas to the oxidizer in this known process of making nitric acid.

The operation of the absorber preferably is sc ,cond'ucted that a slight excess of ammonia is supplied so that the gases leavingthe absorber are slightly alkaline. Under these conditions the gases'leaving the absorber are colorless and consist principally A of the conveying gas and a large amount of Water vaporor steam vaporized from the reaction mixture which is maintained hot by the heat of the reaction. The removal of Water inthe form of steam from the reaction mixture in the absorber serves to concentrate the ammonium. nitrate solution formed up to say 85% which is practically the limit of concentration under the conditions described. Concentra-tion of the ammonium nitrate solution from 85% to 100% and crystallization of the.100%' solution is accomplished inthe grainers 14 in the well-known manner. In order to facilitate the removal of Water, introduced principally with the nitric acid supply, from-the reaction mixture in the absorber the latter' may be insulated or even jacketed for external heating. At the same time the flow of gas through the reaction mixture in the absorber and the evaporation'of Water serve to prevent the reaction mixture from attaming too high.v

a temperature, i. e., the temperature at which ammonium nitrate is descomposed.

Any ammonia in the gas mixture which is not removed in the absorber, the reaction being 'conducted as stated so that the exit gases from the absorbers are slightly alkaline, -is either4 absorbed in the` condensed steam in the condenser 16 and4 recovered from resulting solution in the stripping column 1 and returned to the absorber orsimply passes on with the -'stripping gas through the stripping column and back to' the absorberend therefore is not lost.

and nitric acid and a concentrated solution of ammonium nitrate ready for treatment in the grainerj'sgbeing discharged from the closed syst'einfwlhc transfer of ammonia from the water solution thereof vto the nitric acid neutralizer is accomplished by'a. cyclical flow of an inert gas thus guarding against loss of the nitric acid and ammonia involved in the process.

I claim:

l. Process of making' ammonium nitrate which comprises contacting an inert gas with a Water solution of ammonia, contacting the resulting mixture'of inert gas and ammonia with a solution containing ammonium nitrate, adding nitric acid to the solution of ammonium nitrate and reusing the unabsorbed inert gas forv conveying more ammonia from the Water solution thereof to the solution of ammonium nitrate. j

2. Process of making ammonium nitrate which comprises circulating a stream of an inert gas in a closed cycle including a region of contact Withal water solution of ammonia and a region of contact with awater soinmonia, contacting the resulting mixture of inert gas' and ammonia in continuous flow with a solution of ammonium nitrate, addf ing nitric acid to the solution of ammonium nitrate, and returning the resulting unabsorbed inert gas into contact -with said'body of Water solution of ammonia.

4. Process of making ammonium nitrate which comprises passing 4a stream of gas in a closed gas tight circuit including a region of contact with a Water solution of ammonia, a re ion of contact with a solution of ammonium nitrate, and a region -of contact with cooling and condensing means in succession.-

"5. Process of making ammonium, nitrate as defined claim 4 in which the-region of contact with a solution of ammonium nitrate is" maintained at sub-atmospheric pressure.

6. Process'of making ammonium nitrate which comprises stripping a Water solution of; ammonia. with astream of air, contacting the resulting mixture ofair and ammonia water solution oi ammonia eing stripped,

with a-solutmn of ammonium nitrate main- .and using the air vfor stripping' a.. further v tained atan elevated temperature, adding quantity of water solution of ammonia. l l0 nitric acid to said solution -of ammonium In testimony whereof, Ifaix my signa-` nitrate subjecting the resulting mixture of ture. l l air and water vapor tocooling and condenp Y 4 sation, delivering the condensate into a HENRY HOWARD. 

